OCR B (Salters) F332 Tuesday 4th June 2013 Exam Discussion (Now Closed)

Original post by Welbeck

to produce a aldehyde, do you do reflux then distil but for carboxylic acid, do you reflux, distil and reflux or just reflux? (obviously with acidified potasium dichromate)

Aldehyde: Distill immediately with NO reflux
Carboxylic acid: Reflux

Reply 203

super121

5

Original post by nukethemaly

Heya could you help me with this one question please? I have an idea of what it's supposed to look like but I can't execute it properly.

Ignore whatever I've drawn!

What you have drawn is correct, the would be without a catalyst. For the one with the catalyst, draw another line that is a bit lower (to show that the activation energy is lower).
To show the enthalpy change, just draw a vertical arrow from the reactants to the highest point on the curve.

Reply 204

Original post by super121

What you have drawn is correct, the would be without a catalyst. For the one with the catalyst, draw another line that is a bit lower (to show that the activation energy is lower).
To show the enthalpy change, just draw a vertical arrow from the reactants to the highest point on the curve.

Something like this? I worked it out, but I'm still not convinced if I'll get full marks for it

photo (26).jpg505.7KB

Reply 205

Original post by StephenNaulls

Aldehyde: Distill immediately with NO reflux
Carboxylic acid: Reflux

Hey when I speak about rate of reaction etc, does it sound better to say "more collisions per unit of time" or "frequent collisions" because in every mark scheme its a different story!

Reply 206

super121

5

Original post by nukethemaly

Something like this? I worked it out, but I'm still not convinced if I'll get full marks for it

Yea, it's correct, by delta H would be for the arrows in the middle :smile:

Reply 207

usycool1

19

Original post by nukethemaly

Hey when I speak about rate of reaction etc, does it sound better to say "more collisions per unit of time" or "frequent collisions" because in every mark scheme its a different story!

Either. I prefer "frequent collisions" but both are fine.

Reply 208

krisshP

14

Original post by nukethemaly

Hey sorry I saw your message a bit late! but someone's already helped you out so its all well.

Yeah with ionic equations first thing you do is:

•

write out a balanced equation of the chemical reaction

•

then you write a full ionic equation. To do that: you split all the aqueous reactants and products into their respective ions (don't forget to balance those out based on the balanced equation you previously wrote out)

•

REMEMBER: any solid product will stay the same, and won't split into ions.

•

Then you cancel out any ions which are the same on both sides.

•

Finally always always put the states.

And just a simple shortcut: for all neutralisation reactions of an acid-alkali titration you always get this: H+ + OH- --> H2O as the ionic equation.

It might also be a good idea to make note of common ions that appear every now and again. Like sulfate is SO4^2- and carbonate is CO3^2-, and oxide is O^2-

WTF are you serious? I thought you just split all aqueous reactants into ions? This is so bloody confusing!

Reply 209

krisshP

14

Original post by nukethemaly

Hey sorry I saw your message a bit late! but someone's already helped you out so its all well.

Yeah with ionic equations first thing you do is:

•

write out a balanced equation of the chemical reaction

•

then you write a full ionic equation. To do that: you split all the aqueous reactants and products into their respective ions (don't forget to balance those out based on the balanced equation you previously wrote out)

•

REMEMBER: any solid product will stay the same, and won't split into ions.

•

Then you cancel out any ions which are the same on both sides.

•

Finally always always put the states.

And just a simple shortcut: for all neutralisation reactions of an acid-alkali titration you always get this: H+ + OH- --> H2O as the ionic equation.

It might also be a good idea to make note of common ions that appear every now and again. Like sulfate is SO4^2- and carbonate is CO3^2-, and oxide is O^2-

What do you mean by this?

Reply 210

krisshP

14

Original post by nukethemaly

Hey sorry I saw your message a bit late! but someone's already helped you out so its all well.

Yeah with ionic equations first thing you do is:

•

write out a balanced equation of the chemical reaction

•

then you write a full ionic equation. To do that: you split all the aqueous reactants and products into their respective ions (don't forget to balance those out based on the balanced equation you previously wrote out)

•

REMEMBER: any solid product will stay the same, and won't split into ions.

•

Then you cancel out any ions which are the same on both sides.

•

Finally always always put the states.

And just a simple shortcut: for all neutralisation reactions of an acid-alkali titration you always get this: H+ + OH- --> H2O as the ionic equation.

It might also be a good idea to make note of common ions that appear every now and again. Like sulfate is SO4^2- and carbonate is CO3^2-, and oxide is O^2-

But I thought you only split aqueous reactants?

This is so confusing ahhhhhhhhh

Reply 211

King Hotpie

Original post by nukethemaly

Something like this? I worked it out, but I'm still not convinced if I'll get full marks for it

Does a catalyst not need 2 'humps'? As they work by providing an intermediate step, so there are effectively 2 different activation enthalpies, both of which are lower than the original.

Reply 212

Jlane5000

4

Original post by Jlane5000

Hi can someone please help me with this part of the spec "Explain the risks associated with the storage and transport of the halogens (fluorine to iodine)"

I've gone through all past paper mark schemes and can't compile a complete list. I know they are toxic/corrosive and that they should all be kept away from flames, but are there any specific ones for each halogen?

Cheers :biggrin:

Anyone?

Reply 213

King Hotpie

Fluorine and chlorine are both gases, so they'll spread quickly and be more difficult to clean up? Also more difficult to store. Similar with (liquid) bromine but on a lesser scale.

Reply 214

Jlane5000

4

Original post by King Hotpie

Fluorine and chlorine are both gases, so they'll spread quickly and be more difficult to clean up? Also more difficult to store. Similar with (liquid) bromine but on a lesser scale.

Thanks

Reply 215

Original post by krisshP

WTF are you serious? I thought you just split all aqueous reactants into ions? This is so bloody confusing!

Of course the aqueous products split too, or else how would you expect to cancel out the spectator ions that are the same on BOTH sides?

Reply 216

Original post by krisshP

What do you mean by this?

Say if you have a question that says:
Write an ionic equation for the reaction of barium chloride solution with sodium sulfate solution. A precipitate of barium sulfate forms:

then first step: BaCl2(aq) + Na2SO4(aq) --> BaSO4(s) + 2NaCl (aq)

right?

then next step: split all aqueous products and reactants into its ions:
Ba^2+(aq) + 2Cl^-(aq) + 2Na^+(aq) + SO4^2-(aq) --> BaSO4(s) + 2Na^+ + 2Cl^-

alright, now let me explain why I've put two infront of few of these ions, it's because in the first step you have BaCl2, that means one ion of barium and 2 of chloride, and same for the rest, but for 2NaCl, its two of sodium and 2 of chlorine.

Okay now finally: cancel out the ions that are same on both sides, so your final equation is:
Ba^2+(aq) + SO4^2-(aq) --> BaSO4 (s)

Reply 217

Phteven

Original post by nukethemaly

Hey when I speak about rate of reaction etc, does it sound better to say "more collisions per unit of time" or "frequent collisions" because in every mark scheme its a different story!

I prefer to say more frequent collisions. Since f=1/T, where T is the time period, 'per unit time' would probably also be acceptable. So honestly I don't think it matters.

Reply 218

Original post by krisshP

But I thought you only split aqueous reactants?

This is so confusing ahhhhhhhhh

yes both aqueous reactants and aqueous products, but nothing solid. BECAUSE IF THEY'RE IN A SOLUTION AQUEOUS THINGS ARE BOUND TO DISSOLVE (HENCE SPLIT INTO THEIR IONS BECAUSE THEY'RE HYDRATED NOW) AND THE SOLID WONT. THE SOLID JUST SETTLES DOWN.

Reply 219